1. Field of the Invention
The present invention relates to a new catalysts for the partial oxidation of hydrocarbons.
2. Related Art
The catalytic partial oxidation of hydrocarbons (CPO), natural gas or methane to synthesis gas resulting in mixtures of hydrogen (H2) and carbon monoxide (CO) in various proportions, has been processed for many years. While currently limited as an industrial process, the partial oxidation is also of interest for the significant released heat and for the use of smaller reactors. More particularly, the partial oxidation of methane at short residence time is a goal to reach synthesis gas using an alternative process to the steam reforming process, which is today the most popular one.
Synthesis gas can be used as feed for fuel cell or as a reducing atmosphere in the metallurgic industry but it is mainly the key step for activation of methane for the indirect production of methanol and middle distillate in the petrochemical and chemical industries.
The advantage of the catalytic partial oxidation of methane is mainly its strong exothermic character in the short residence time. Both parameters allow producing synthesis gas with lower investment cost without delivering large quantities of external energy.
Nevertheless, because this strong exothermic character of the total oxidation reactions, the temperature of the catalytic bed reaches more than well above 1000° C.
There is thus a need for very stable catalyst in terms of metal sintering and support resistance.
Furthermore, as the catalyst activity affects the thermal profile of the reactor, a careful modulation is therefore required to avoid hot spot in the reactor which can light on the homogeneous reaction.
A novel approach relates to the possibility of introducing the metal in the crystallographic structure of a given material and then to activate the catalyst by reducing the metal “in situ” or under hydrogen flow. This allows in some case to develop a strong interaction between metal and surface, Some of these catalysts have a Perovskite structure.
U.S. Pat. No. 5,149,516 discloses the partial oxidation of methane to produce carbon monoxide and hydrogen using a Perovskite catalyst, such as LaCoO3.
U.S. Pat. No. 5,447,705 discloses a catalyst for the partial oxidation of methane or of a gaseous mixture containing methane, said catalyst preferably having a Perovskite structure with LaFeNi as a cation composition. However, in the reported examples it is very difficult to balance the structure stability. On one hand, if the reducible metal (Ni and Co) is present in large amount, the structure is completely reduced and the Perovskite structure becomes unstable. On the other hand, if the reducible cation is present in low amount, the catalytic activity is poor and does not allow to work with short residence time.
U.S. Pat. No. 6,110,861 discloses a two-part catalyst comprising a dehydrogenation portion and an oxide-ion conducting portion.
WO 0160742 discloses a catalysts and a processes for the catalytic conversion of hydrocarbons to carbon monoxide and hydrogen employing new families of chromium-rare earth based catalysts.
Today, none of the existing catalytic partial oxidation processes is able to provide a sufficiently high conversion of the reactant gas together with a high selectivity of CO and H2 reaction products, without using high quantities of rare and costly catalysts, nor without experiencing adverse effects such as an excessive coking of the catalyst, or a premature catalyst failure by its lack of heat resistance or by its mechanical instability or even by the mechanical instability of its structure.
That is why there is a continuing need for new catalysts that are mechanically stable and retains a high level of activity and selectivity to CO and H2 products under conditions of high temperature, without excessive coking.
The inventors have found that the catalysts of the present invention overcome some of these drawbacks.